1. Field of the Invention
The present invention relates to a device for controlling clock selection in a redundant clock system and, more particularly, to a clock selection control device designed to prevent the selection of a failed clock and the stoppage of device functions in the event of failure of a clock selection controller.
2. Description of the Related Art
In recent years, transmission/communication apparatus, information processing apparatus and other equipment for processing digital signals have been increasing in functional complexity, in accordance with which enhancing system reliability has become a major consideration in designing these apparatus. To achieve this, techniques have been employed wherein the master clock of the device is designed with a redundant circuit and, within each device section operated by the clock, control is performed for the selection between the current and spare clock in the event of clock failure.
In one such redundant master clock selection system, a selector for selecting a clock is provided within each device section, and a clock selection controller is provided common to the entire device. In such a system, information concerning the detection of a clock stoppage at the selector input in each device section is supplied to the clock selection controller, which then makes a decision as to which of the clocks is to be selected. Based on this decision, the clock selection controller supplies selector control information to the device section. In accordance with the selector control information, the selector within the device section switches the clock path from the current clock to the spare clock.
The above prior art clock selection system, however, has had the problem that if the clock selection controller becomes faulty, or if the clock selection controller is disconnected during maintenance or is not connected correctly for operation, for example, the switching by the selector in each device section may not be accomplished properly, resulting in the stoppage of device functions.